Bill Watterson, the cartoonist and creator of the beloved "Calvin and Hobbes," has lived a reclusive lifestyle after ending his popular comic strip back in 1995. Since sending his popular cartoon duo down a snowy hill to explore the world over 18 years ago, Watterson has shied away from interviews and hasn't picked up a pen or drawn another published comic strip.

That is, until now.

This week, "Pearls Before Swine" cartoonist Stephan Pastis secretly invited Watterson to guest draw several comic strips under the guise of second-grader Libby.

Pastis contacted Watterson when the "Pearls Before Swine" cartoonist was traveling through Cleveland on a book tour, never expecting to get a reply.

But he did.

"Just getting an email from Bill Watterson is one of the most mind-blowing, surreal experiences I have ever had," Pastis wrote on his blog. "Bill Watterson really exists? And he sends email? And he’s communicating with me?"

Not only did Watterson write back, he offered a suggestion for a comic idea the two could collaborate on.

"He said he knew that in my strip, I frequently make fun of my own art skills," Pastis wrote. "And that he thought it would be funny to have me get hit on the head or something and suddenly be able to draw. Then he’d step in and draw my comic strip for a few days."

Here are the strips (syndicated by Universal uClick), which appeared in newspapers across the country (including the pages of the Inquirer):

So what lured Watterson back to the comics page?

“Several years ago, when Stephan did one of his strips that mocked his own drawing ability and mentioned my strip in comparison, I thought it might be funny for me to ghost ‘Pearls’ sometime, just to flip it all on its head,” a goateed Watterson told Michael Cavna of the Washington Post. ,Watterson envisioned using the opportunity to help fellow cartoonist Richard Thompson, creator of "Cul de Sac," who is suvvering from Parkinson's disease.

“I thought maybe Stephan and I could do this goofy collaboration and then use the result to raise some money for Parkinson’s research in honor of Richard Thompson," Watterson told Cavna.

“I had expected to just mess around with his characters while they did their usual things, but Stephan kept setting up these situations that required more challenging drawings . . . so I had to work a lot harder than I had planned to! It was a lot of fun.”

Chris Sparks, the lead fundraiser and cheerleader for Team Cul de Sac, convinced Watterson to contribute an original painting as part of a book featurting famous cartoonists, Watterson's first public art in 16 years. The publicity surrounding Watterson's donation helped Team Cul de Sac raise nearly $125k for the Michael J. Fox Foundation.

"Bill has been such a strong supporter that he wanted to do something else for us," Sparks said. "I had the great privilege of having breakfast with Bill on June 4th and handing him the morning paper. I watched him read his first newspaper work in 19 years. I don’t think he’d mind me saying he was grinning from ear to ear. I know I was."